1. Field of the Invention
The present invention relates to a heat treatment technique by which a substrate to be processed is accommodated in a processing chamber and processing is performed in a heated state by a heater. For example, the present invention relates to a temperature detecting apparatus, a substrate processing apparatus and a method of manufacturing a semiconductor device, which are used for performing heat treatment on a semiconductor substrate (for example, a semiconductor wafer) on which a semiconductor integrated circuit device (hereinafter referred to as “IC”) is fabricated, such as oxidation processing or diffusion processing, or reflow processing or annealing processing for activation or planarization of a carrier after ions have been implanted, or film forming processing by thermal chemical vapor deposition (CVD) reaction.
2. Description of the Related Art
In manufacturing an IC, a batch type vertical heat treatment apparatus is widely used in order to heat-treat a substrate. In a processing furnace of the heat treatment apparatus of the related art, a boat on which a plurality of wafers are mounted is inserted from a lower portion thereof in a vertical reaction tube of a substantially cylindrical shape with its upper end closed and its lower end open and the wafers disposed on the boat are heat-treated by a heater installed so as to surround an outside of the reaction tube. The plurality of wafers are in a horizontal posture on the boat, and stacked and held in a multi-stage at a state aligned to a center of each wafer. A soaking tube of a substantially cylindrical shape with its upper end closed and its lower end open is installed between the reaction tube and the heater. The soaking tube is formed uniformly so that heat radiated form the heater to the wafer does not vary depending on a position.
A temperature detecting tube for detecting a temperature is installed between the soaking tube and the reaction tube, and an output of the heater, that is, a temperature of the wafer is controlled to a predetermined temperature based on a temperature detected by the temperature detecting tube. A thermocouple, which is a temperature detection device, is inserted into an inside of the temperature detecting tube and the thermocouple is connected to a temperature control portion through a signal line. In a vertical heat treatment furnace including a reaction tube and a heater, a technique of installing a thermocouple for detecting a temperature of the processing furnace has been disclosed (see Japanese Patent Unexamined Application No. 2009-117618).
A method of installing a thermocouple in the related art will be described with reference to FIGS. 12 to 15. FIG. 12 is a diagram illustrating a structure of a thermocouple of the related art, and the thermocouple between a reaction tube and a soaking tube is viewed from a center of a processing furnace. FIG. 13 is a cross-sectional view taken along line A-A of FIG. 12, and a horizontal sectional view of the thermocouple. FIG. 14 is a vertical sectional view viewed from the side of the thermocouple of FIG. 12. FIG. 15 is a diagram illustrating a support state of a thermocouple of the related art. In an example of FIG. 12, there are five thermocouples, that is, a first thermocouple including a thermocouple junction portion 423a, a second thermocouple including a thermocouple junction portion 423b, a third thermocouple including a thermocouple junction portion 423c, a fourth thermocouple including a thermocouple junction portion 423d, and a fifth thermocouple including a thermocouple junction portion 423e. The first thermocouple and the fourth thermocouple are inserted into a protection tube 431a, the second thermocouple and the fifth thermocouple are inserted into a protection tube 431b, and the third thermocouple is inserted into a protection tube 431c. 
The first thermocouple is for temperature detection of an uppermost heater (U zone heater) of the processing furnace, the second thermocouple is for temperature detection of a heater (CU zone heater) immediately below the U zone heater, the third thermocouple is for temperature detection of a heater (C zone heater) immediately below the CU zone heater, the fourth thermocouple is for temperature detection of a heater (CL zone heater) immediately below the C zone heater, and the fifth thermocouple is for temperature detection of a lowermost heater (L zone heater) of the processing furnace.
As shown in FIG. 13, which is a cross-sectional view taken along line A-A of FIG. 12, the fourth thermocouple is located at the front (a central side of the processing furnace) in the protection tube 431a, and the first thermocouple is located at the rear. In addition, the fifth thermocouple is located at the front in the protection tube 431b and the second thermocouple is located at the rear. The cross section of an insulation rod 432a of the first thermocouple is elliptical, two holes penetrate through the cross section, and a thermocouple wire 421a of a plus side and a thermocouple wire 422a of a minus side are each inserted and accommodated into the two holes. Insulation rods 432b to 432e of the second thermocouple to the fifth thermocouple are also the same. The thermocouple wire is a wire part of the thermocouple that converts a temperature to a thermal electromotive force.
The first thermocouple is configured to include the thermocouple wire 421a of the plus side and the thermocouple wire 422a of the minus side, the thermocouple junction portion 423a in which the thermocouple wire 421a and the thermocouple wire 422a are jointed at a front end portion thereof, the insulation rod 432a for insulating the thermocouple wire 421a and the thermocouple wire 422a from each other, and a cap 434a for closing an upper end of the insulation rod 432a. 
FIG. 14 is a side view of the first thermocouple. As shown in FIG. 14, in the thermocouple wire 421a and the thermocouple wire 422a (the thermocouple wire 422a is not shown), an inside of a soaking tube 221 extends in a vertical direction, and the thermocouple junction portion 423a is installed on upper ends thereof. In order to avoid a short circuit, the thermocouple wire 421a and the thermocouple wire 422a are each accommodated in the two holes of the insulation rod 432a. The cap 434a is installed on the upper end of the insulation rod 432a so as to seal the thermocouple junction portion 423a. The insulation rod 432a is inserted into the protection tube 431a, and the lower portion of the protection tube 431a is fixed by a protection tube holder 436. In addition, the lower portion of the insulation rod 432a extending in the vertical direction is in contact with the insulation rod 433a extending in the horizontal direction, and the insulation rod 433a is fixed by the protection tube holder 436. The thermocouple wire 421a and the thermocouple wire 422a, which pass through the inside of the insulation rod 432a in the vertical direction, turn 90° from the lower end of the insulation rod 432a and pass through the inside of the insulation rod 433a in a horizontal direction to be connected to a temperature control portion (not shown).
Similar to the first thermocouple, the second thermocouple is configured to include a thermocouple wire 421b of a plus side and a thermocouple wire 422b of a minus side, the thermocouple junction portion 423b in which the thermocouple wire 421b and the thermocouple wire 422b are jointed at a front end portion thereof, the insulation rod 432b for insulating the thermocouple wire 421b and the thermocouple wire 422b from each other, and a cap 434b for closing an upper end of the insulation rod 432b. The third thermocouple is configured to include a thermocouple wire 421c of a plus side and a thermocouple wire 422c of a minus side, the thermocouple junction portion 423c in which the thermocouple wire 421c and the thermocouple wire 422c are jointed at a front end portion thereof, the insulation rod 432c for insulating the thermocouple wire 421c and the thermocouple wire 422c from each other, and a cap 434c for closing an upper end of the insulation rod 432c. The fourth thermocouple is configured to include a thermocouple wire 421d of a plus side and a thermocouple wire 422d of a minus side, the thermocouple junction portion 423d in which the thermocouple wire 421d and the thermocouple wire 422d are jointed at a front end portion thereof, the insulation rod 432d for insulating the thermocouple wire 421d and the thermocouple wire 422d from each other, and a cap 434d for closing an upper end of the insulation rod 432d. The fifth thermocouple is configured to include a thermocouple wire 421e of a plus side and a thermocouple wire 422e of a minus side, the thermocouple junction portion 423e in which the thermocouple wire 421e and the thermocouple wire 422e are jointed at a front end portion thereof, the insulation rod 432e for insulating the thermocouple wire 421e and the thermocouple wire 422e from each other, and a cap 434e for closing an upper end of the insulation rod 432e. 
In addition, as shown in FIG. 15, in the related art, a thermocouple wire 421 of a plus side and a thermocouple wire 422 of a minus side are fixed by a thermocouple wire support portion 424 disposed therebelow. More specifically, the thermocouple wire 421 and the thermocouple wire 422 are bent to have an L shape in an L-shaped portion including an insulation rod 432 and an insulation rod 433. Accordingly, the lower portions of the thermocouple wire 421 and the thermocouple wire 422 are substantially fixed in the vertical direction. In addition, the thermocouple wires 421a to 421e are collectively referred to as the thermocouple wire 421, the thermocouple wires 422a to 422e as the thermocouple wire 422, the thermocouple junction portions 423a to 423e as the thermocouple junction portion 423, the insulation rods 432a to 432e as the insulation rod 432, the insulation rods 433a to 433e as the insulation rod 433, and the caps 434a to 434e as the cap 434.
FIG. 16 is a diagram illustrating an expansion and contraction state of a thermocouple of the related art, FIG. 16a represents a standby state (500° C.) before heat treatment, FIG. 16b represents a process state (1200° C.) during heat treatment, and FIG. 16c represents a standby state (500° C.) after heat treatment. When the standby state of FIG. 16a comes to the heat treatment state of FIG. 16b, the thermocouple wires 421 and 422 and the insulation rod 432 are heat-expanded, and the thermocouple wires protrude from the upper end of the insulation rod 432, such that the thermocouple wires 421 and 422 are lengthened by ΔL. Since the protrusion amount ΔL is determined by an expansion difference between the thermocouple wires 421 and 422 and the insulation rod 432, an insulation rod material of a small expansion difference is selected. When the heat treatment state of FIG. 16b comes to the standby state of FIG. 16c, the thermocouple wires 421 and 422 are heat contracted, such that the thermocouple wires 421 and 422 are shortened by ΔL to thus return to an original length.
When heat expansion and heat contraction are repeated, a displacement or entanglement in grain boundaries of the thermocouple wire 421 or 422 occurs due to a self-weight of the thermocouple wire 421 or 422, or a change over time such as a frictional force with the insulation rod 432. The displacement of grain boundaries means that crystal grains of the thermocouple wire 421 or 422 are bloated by heat treatment, and thus grain boundaries between adjacent grains are deviated by stress due to the heat expansion and heat contraction. FIG. 17 is a diagram illustrating a state in which a thermocouple of the related art is broken, FIG. 17a illustrates a standby state, and FIG. 17b illustrates heat treatment state. When the standby state of FIG. 17a and the heat treatment state of FIG. 17b are repeated, a wire deformation portion 411 is generated, for example, because the thermocouple wire 422 is stretched, and a frictional force with the insulation rod 432 is increased. In addition, the insulation rod 432 is spaced upwardly from the insulation rod 433. In addition, when changes progress over time, as shown in FIG. 17c, during the heat contraction, a binding force in which the thermocouple wire 422 is bound to the insulation rod 432 become stronger, and thus tensile stress to the thermocouple wire 421 increases. Eventually, the tensile strength of the thermocouple wire 422 becomes excessive, and thus the thermocouple wire 421 is disconnected in a disconnection portion 412.
In addition, in the thermocouple installing method of the related art, as described above, since the lower portion of the thermocouple wire 421 or 422 is fixed, the position of the thermocouple junction portion 423, that is, the temperature measurement position is significantly changed by the heat expansion of the thermocouple wire 421 or 422. For example, when a length of the thermocouple wire is 1,500 mm and an ambient temperature is about 1,200° C., the temperature measurement position is shifted by about 19 mm. For this reason, accurate temperature measurement is difficult, and appropriate temperature control is not easy.